@@ -86,7 +86,7 @@ exercises.  Feel free to look at this if you need a hint.  To get the
 most out of the course however, you should try to create your own
 solutions first.
 
-[Contents](Contents.md)
+[Contents](Contents.md) \| [Next (1 Introduction to Python)](01_Introduction/00_Overview.md)
 
 
 
 
@@ -61,7 +61,7 @@ will be able to use it everywhere else.
 
 ### Exercise 1.1: Using Python as a Calculator
 
-On your machine, start Python and use it as a calulator to solve the
+On your machine, start Python and use it as a calculator to solve the
 following problem.
 
 Lucky Larry bought 75 shares of Google stock at a price of $235.14 per
@@ -145,6 +145,11 @@ the class by typing in code slowly and thinking about it--not cut and pasting.
 
 ### Exercise 1.4: Where is My Bus?
 
+Note: This was a whimsical example that was a real crowd-pleaser when
+I taught this course in my office.  You could query the bus and then
+literally watch it pass by the window out front.  Sadly, APIs rarely live
+forever and it seems that this one has now ridden off into the sunset. --Dave
+
 Try something more advanced and type these statements to find out how
 long people waiting on the corner of Clark street and Balmoral in
 Chicago will have to wait for the next northbound CTA \#22 bus:
 
@@ -58,7 +58,7 @@ interact with the interpreter.
 Let's take a closer look at the elements of the REPL:
 
 - `>>>` is the interpreter prompt for starting a new statement.
-- `...` is the interpreter prompt for continuing a statements. Enter a blank line to finish typing and run the statements.
+- `...` is the interpreter prompt for continuing a statement. Enter a blank line to finish typing and run what you've entered.
 
 The `...` prompt may or may not be shown depending on your environment. For this course,
 it is shown as blanks to make it easier to cut/paste code samples.
@@ -241,7 +241,7 @@ while num_bills * bill_thickness < sears_height:
     day = day + 1
     num_bills = num_bills * 2
 
-print('Number of days', days)
+print('Number of days', day)
 ```
 
 The statements indented below the `while` will execute as long as the expression after the `while` is `true`.
@@ -257,7 +257,7 @@ while num_bills * bill_thickness < sears_height:
     day = day + 1
     num_bills = num_bills * 2
 
-print('Number of days', days)
+print('Number of days', day)
 ```
 
 Indentation groups the following statements together as the operations that repeat:
 
@@ -77,7 +77,7 @@ c = -1.345e-10
 Floats are represented as double precision using the native CPU representation [IEEE 754](https://en.wikipedia.org/wiki/IEEE_754).
 This is the same as the `double` type in the programming language C.
 
-> 17 digits or precision
+> 17 digits of precision  
 > Exponent from -308 to 308
 
 Be aware that floating point numbers are inexact when representing decimals.
@@ -106,7 +106,7 @@ x ** y     Power
 abs(x)     Absolute Value
 ```
 
-Theses are the same operators as Integers, except for the bit-wise operators.
+These are the same operators as Integers, except for the bit-wise operators.
 Additional math functions are found in the `math` module.
 
 ```python
@@ -213,14 +213,15 @@ Modify the program so that extra payment information can be more generally handl
 Make it so that the user can set these variables:
 
 ```python
-extra_payment_start_month = 60
+extra_payment_start_month = 61
 extra_payment_end_month = 108
 extra_payment = 1000
 ```
 
 Make the program look at these variables and calculate the total paid appropriately.
 
-How much will Dave pay if he pays an extra $1000/month for 4 years starting in year 5 of the mortgage?
+How much will Dave pay if he pays an extra $1000/month for 4 years starting after the first
+five years have already been paid?
 
 ### Exercise 1.10: Making a table
 
@@ -234,15 +235,16 @@ The output should look something like this:
 4 10736.44 497581.83
 5 13420.55 496970.98
 ...
-308 875705.88 674.44
-309 878389.99 -2006.86
-Total paid 878389.99
-Months 309
+308 874705.88 3478.83
+309 877389.99 809.21
+310 880074.1 -1871.53
+Total paid 880074.1
+Months 310
 ```
 
 ### Exercise 1.11: Bonus
 
-While you’re at it, fix the program to correct the for overpayment that occurs in the last month.
+While you’re at it, fix the program to correct for the overpayment that occurs in the last month.
 
 ### Exercise 1.12: A Mystery
 
 
@@ -2,7 +2,7 @@
 
 # 1.4 Strings
 
-This section introduces way to work with text.
+This section introduces ways to work with text.
 
 ### Representing Literal Text
 
@@ -28,8 +28,8 @@ Normally strings may only span a single line. Triple quotes capture all text enc
 including all formatting.
 
 There is no difference between using single (') versus double (")
-quotes.  The same type of quote used to start a string must be used to
-terminate it.
+quotes. *However, the same type of quote used to start a string must be used to
+terminate it*.
 
 ### String escape codes
 
@@ -134,7 +134,7 @@ t = s.replace('Hello' , 'Hallo')   # 'Hallo world'
 **More string methods:**
 
 Strings have a wide variety of other methods for testing and manipulating the text data.
-This is small sample of methods:
+This is a small sample of methods:
 
 ```python
 s.endswith(suffix)     # Check if string ends with suffix
@@ -144,7 +144,7 @@ s.isalpha()            # Check if characters are alphabetic
 s.isdigit()            # Check if characters are numeric
 s.islower()            # Check if characters are lower-case
 s.isupper()            # Check if characters are upper-case
-s.join(slist)          # Joins lists using s as delimiter
+s.join(slist)          # Join a list of strings using s as delimiter
 s.lower()              # Convert to lower case
 s.replace(old,new)     # Replace text
 s.rfind(t)             # Search for t from end of string
 
@@ -157,7 +157,7 @@ t = sorted(s)               # s unchanged, t holds sorted values
 >>> nums * 2
 [1, 2, 3, 4, 5, 1, 2, 3, 4, 5]
 >>> nums + [10, 11, 12, 13, 14]
-[1, 2, 3, 4, 5, 10, 11, 12, 13, 14] >>>
+[1, 2, 3, 4, 5, 10, 11, 12, 13, 14]
 ```
 
 Specifically, lists don't represent vectors/matrices as in MATLAB, Octave, R, etc.
 
@@ -220,14 +220,17 @@ Try it:
 
 ```python
 >>> import gzip
->>> with gzip.open('Data/portfolio.csv.gz') as f:
+>>> with gzip.open('Data/portfolio.csv.gz', 'rt') as f:
     for line in f:
         print(line, end='')
 
 ... look at the output ...
 >>>
 ```
 
+Note: Including the file mode of `'rt'` is critical here.  If you forget that,
+you'll get byte strings instead of normal text strings.
+
 ### Commentary:  Shouldn't we being using Pandas for this?
 
 Data scientists are quick to point out that libraries like
 
@@ -72,8 +72,8 @@ Exceptions can be caught and handled.
 To catch, use the `try - except` statement.
 
 ```python
-for line in f:
-    fields = line.split()
+for line in file:
+    fields = line.split(',')
     try:
         shares = int(fields[1])
     except ValueError:
 
@@ -58,7 +58,7 @@ Sometimes the `()` are omitted in the syntax.
 s = 'GOOG', 100, 490.1
 ```
 
-Special cases (0-tuple, 1-typle).
+Special cases (0-tuple, 1-tuple).
 
 ```python
 t = ()            # An empty tuple
@@ -338,7 +338,7 @@ above. Change the number of shares to 75.
 ```python
 >>> d['shares'] = 75
 >>> d
-{'name': 'AA', 'shares': 75, 'price': 75}
+{'name': 'AA', 'shares': 75, 'price': 32.2 }
 >>>
 ```
 
 
@@ -52,9 +52,10 @@ An example when reading records from a file.
 records = []  # Initial empty list
 
 with open('Data/portfolio.csv', 'rt') as f:
+    next(f) # Skip header
     for line in f:
         row = line.split(',')
-        records.append((row[0], int(row[1])), float(row[2]))
+        records.append((row[0], int(row[1]), float(row[2])))
 ```
 
 ### Dicts as a Container
@@ -105,6 +106,11 @@ with open('Data/prices.csv', 'rt') as f:
         prices[row[0]] = float(row[1])
 ```
 
+Note: If you try this on the `Data/prices.csv` file, you'll find that
+it almost works--there's a blank line at the end that causes it to
+crash.  You'll need to figure out some way to modify the code to
+account for that (see Exercise 2.6).
+
 ### Dictionary Lookups
 
 You can test the existence of a key.
@@ -189,12 +195,14 @@ unique = set(names)
 Additional set operations:
 
 ```python
-names.add('CAT')        # Add an item
-names.remove('YHOO')    # Remove an item
-
-s1 | s2                 # Set union
-s1 & s2                 # Set intersection
-s1 - s2                 # Set difference
+unique.add('CAT')        # Add an item
+unique.remove('YHOO')    # Remove an item
+
+s1 = { 'a', 'b', 'c'}
+s2 = { 'c', 'd' }
+s1 | s2                 # Set union { 'a', 'b', 'c', 'd' }
+s1 & s2                 # Set intersection { 'c' }
+s1 - s2                 # Set difference { 'a', 'b' }
 ```
 
 ## Exercises
@@ -309,7 +317,7 @@ Experiment with this new function in the same manner as you did in
 Exercise 2.4.
 
 ```python
->>> portfolio = read_portfolio('portfolio.csv')
+>>> portfolio = read_portfolio('Data/portfolio.csv')
 >>> portfolio
 [{'name': 'AA', 'shares': 100, 'price': 32.2}, {'name': 'IBM', 'shares': 50, 'price': 91.1},
     {'name': 'CAT', 'shares': 150, 'price': 83.44}, {'name': 'MSFT', 'shares': 200, 'price': 51.23},
@@ -335,7 +343,7 @@ accessed by key names instead of numeric column numbers.  This is
 often preferred because the resulting code is easier to read later.
 
 Viewing large dictionaries and lists can be messy. To clean up the
-output for debugging, considering using the `pprint` function.
+output for debugging, consider using the `pprint` function.
 
 ```python
 >>> from pprint import pprint
@@ -437,9 +445,9 @@ interactively to make sure it works:
 ### Exercise 2.7: Finding out if you can retire
 
 Tie all of this work together by adding a few additional statements to
-your `report.py` program that compute gain/loss. These statements
+your `report.py` program that computes gain/loss. These statements
 should take the list of stocks in Exercise 2.5 and the dictionary of
-prices in Exercise 2.6 and computes the current value of the portfolio
+prices in Exercise 2.6 and compute the current value of the portfolio
 along with the gain/loss.
 
 [Contents](../Contents.md) \| [Previous (2.1 Datatypes)](01_Datatypes.md) \| [Next (2.3 Formatting)](03_Formatting.md)